1. Field of the Invention
The present invention generally relates to a system board device and, more particularly, to a printed-circuit board reinforcing member for reinforcing a printed-circuit board and a system board device using such a printed circuit board.
A large-scale computer is provided with a system board device comprising a mother bard and a plurality of daughter boards mounted on the mother board. A plurality of RAMs are mounted on each of the daughter boards. Additionally, a plurality of multi-chip modules, each of which has a pin grid-array structure, are mounted on the mother board. The multi-chip module having the pin grid-array structure is mounted on the mother board by a plurality of pins being soldered to respective terminals formed on the mother board. Such a multi-chip module has a relatively large vertical cross section having a side of which length is as long as 100 mm. Accordingly, if the mother board is warped, a displacement of the pins from the mother board is large. Thus, there is a problem in that a reliability of mounting is decreased. Additionally, In the system board device, the mother board is modified if necessary. Accordingly, the system board device preferably has a structure in which replacement of the multi-chip module and modification of the mother board are considered.
2. Description of the Related Art
FIG. 1 is a perspective view of a conventional system board device 10. In FIG. 1, the system board device 10 includes a mother board 11, a mother-board reinforcing member 12 having a square-frame shape and a multi-chip module 20. The mother-board reinforcing member 12 is fixed to a front surface of the mother board 11 in an area in which the multi-chip module 20 is placed. The mother-board reinforcing member 12 is fixed to the mother board 11 by screws 13 provided on each corner of the mother-board reinforcing member 12. Accordingly, the multi-chip module 20 having a pin grid array is located inside the mother-board reinforcing member 12. Since the mother-board reinforcing member 12 is fixed by screws 13 at each corner portion of the mother-board reinforcing member 12, an area in which the multi-chip module 20 is positioned is reinforced by the mother-board reinforcing member 12. In such a structure, the mother board 11 is hardly warped when a thermal stress is generated in the mother board 11. Thereby, soldered portions between the pins of the multi-chip module 20 and the terminals formed on the front surface of the mother board 11 are positively prevented from being destroyed.
FIG. 2 is a perspective view of another conventional system board device 30. The system board device 30 comprises the mother bard 11, a mother-board reinforcing member 31 having a square-frame shape and the multi-chip module 20 having pins 21 to be soldered to the terminals of the mother board 11. Unlike the mother-board reinforcing member 12 shown in FIG. 1, the mother-board reinforcing member 31 is fixed to a back surface of the mother board 11. The mother-board reinforcing member 31 is located in an area in which the multi-chip module 20 is mounted, and is fixed by screws 32 at each corner portion of the mother-board reinforcing member 31. That is, the mother-board reinforcing member 31 is fixed to the mother board 11 in a position opposite to the multi-chip module 20. As shown in an enlarged view in FIG. 2, each of the pins 21 is connected to the respective terminal 33 of the mother board 11 by a solder 34.
In the system board device 10 shown in FIG. 1, a space 41 is needed between the multi-chip module 20 and the mother-board reinforcing member 12 that surrounds the multi-chip module 20 so that a nozzle 40 having a square-frame shape can be inserted between the multi-chip module 20 and the mother-board reinforcing member 12 so as to blow hot air to melt a solder. Accordingly, the size of the mother-board reinforcing member 12 is increased. Thus, if a plurality of multi-chip modules 20 are mounted on the mother board 11, a distance between the adjacent multi-chip modules 20 is increased, which results in a low efficiency of mounting.
Additionally, a wire 42 for modification of the mother board 11 must run over a top surface of the mother-board reinforcing member 12, and it is difficult to fix the wire 42 to the mother board 11. Accordingly, the wire tends to be unintentionally cut off when the multi-chip module 20 is removed from the mother board 11 by using the above-mentioned nozzle 40.
On the other hand, in the system board device 30 shown in FIG. 2, since the mother-board reinforcing member 31 is mounted on the back surface of the mother board 11, a plurality of multi-chip modules can be efficiently arranged on the mother board 11. However, since the mother-board reinforcing member 31 protrudes in a direction opposite to the multi-chip module 20, an overall height H of the system board device 30 is larger than an overall height of the system module device 10 shown in FIG. 1. This is not preferable when the system board device 30 must be accommodated in a small and restricted space of a large-scale computer. Additionally, since the mother-board reinforcing member 31 is mounted on the back surface which is opposite to the front surface on which the multi-chip module 20 is mounted, a capability for restricting a warp due to a thermal stress is lower than that of the mother-board reinforcing member 12 which is mounted on the same surface on which the multi-chip module 20 is mounted. Thus, a reliability of the soldered connection between the pins 21 of the multi-chip module 20 and the terminals 33 formed on the mother board 11 is decreased.